A solid catalyst component containing magnesium, titanium, an electron donor compound, and halogen as essential components used for the polymerization of olefins such as propylene has been known in the art. Also, a large number of methods for olefin polymerization by polymerization or copolymerization of propylene, in the presence of an olefin polymerization catalyst comprising the above solid catalyst components, an organoaluminum compound, and an organosilicon compound, have been proposed. For example, Japanese Unexamined Patent Publication No. (hereinafter referred to as JP-A) 63310/1982 and JP-A No. 63311/1982 propose a method for polymerization of olefins, particularly olefins with three or more carbon atoms, in which a combined catalyst comprising solid catalyst components containing a magnesium compound, titanium compound, and an electron donor, and an organoaluminum compound and an organosilicon compound having a Si—O—C linkage is used. However, because these methods are not necessarily satisfactory for producing high stereoregularity polymers at a high yield, improvement of these methods has been desired.
JP-A No. 3010/1988 proposes an olefin polymerization catalyst and a polymerization method. The olefin polymerization catalyst comprises a solid catalyst component, obtained by processing a powder produced from dialkoxy magnesium, aromatic dicarboxylic acid diester, aromatic hydrocarbon, and titanium halide with heat, an organoaluminum compound, and an organosilicon compound.
JP-A No. 315406/1989 proposes another olefin polymerization catalyst and a polymerization method using this catalyst. The olefin polymerization catalyst comprises a solid catalyst component prepared by bringing a titanium tetrachloride into contact with a suspension formed by a diethoxymagnesium with an alkylbenzene, adding phthalic dichloride thereto to react to obtain a solid product, and further contacting the resulting solid product with a titanium tetrachloride in the presence of an alkylbenzene, an organic aluminum compound and an organic silicon compound.
All of the above-described conventional technologies have attained certain results in improving the catalyst activity to the extent of permitting dispensing with an ash-removal step for removing catalyst residues such as chlorine and titanium from the formed polymers, improving the yield of stereoregularity polymers, and improving the durability of the catalyst activity during the polymerization.
The polymers produced using these catalysts are used in a variety of applications including formed products such as parts of vehicles and household electric appliances, containers, and films. These products are manufactured by melting polymer powders produced by the polymerization and by forming the melted polymer using any one of various molds. In manufacturing formed products, particularly large products, by injection molding or the like, melted polymers are sometimes required to have high fluidity (melt flow rate). Accordingly, a number of studies have been undertaken to increase the melt flow rate of polymers.
The melt flow rate greatly depends on the molecular weight of the polymers. In the polymer industry, hydrogen is generally added as a molecular weight regulator for polymers in the polymerization of olefins. In this instance, a large quantity of hydrogen is usually added to produce low molecular weight polymers which are the polymers having a high melt flow rate. However, the quantity of hydrogen which can be added is limited because of the pressure resistance of the reactor from the viewpoint of safety. In order to add a larger amount of hydrogen, the partial pressure of monomers to be polymerized has to be decreased. The decrease in the partial pressure, however, is accompanied by a decrease in productivity. Additionally, use of a large amount of hydrogen may bring about a problem of cost. Development of a catalyst capable of producing polymers with a high melt flow rate by using a smaller amount of hydrogen, in other words, a catalyst which has a high activity to hydrogen and produces a highly stereoregular polymer, while maintaining high yield performance has therefore been desired. Conventional technologies have been insufficient in solving these requirements.
To achieve this objective, JP-A No. 218932/1998 discloses a catalyst for polymerization of olefins comprising a halogen-containing organosilicon compound of the following formula (I) and an organosilicon compound of the following formula (II) as organosilicon compounds:Si(OR8)4−nZn  (I)wherein R8 individually represents an alkyl group having 1 to 4 carbon atoms, a cycloalkyl group, a phenyl group, a vinyl group, an allyl group, or an aralkyl group, Z indicates a halogen atom, and n is an integer of 1 to 3;R9tSi(OR10)4−t  (II)wherein the group R9 individually represent an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group, a phenyl group, a vinyl group, an allyl group, or an aralkyl group, R10 individually represents an alkyl group having 1 to 4 carbon atoms, a cycloalkyl group, a phenyl group, a vinyl group, an allyl group, or an aralkyl group, and t is 0 or an integer of 1 to 3.
This olefin polymerization catalyst is not yet satisfactory for providing olefin polymers with a sufficient melt flow rate, although certain improvement is seen in the catalyst activity to hydrogen.
Therefore, an object of the present invention is to provide an olefin polymerization catalyst having a high activity to hydrogen and exhibiting high catalytic activity, yield performance, and capability of producing polymers with stereoregularity equivalent to conventional catalyst for polymerization of olefins.